Rename plugins to Extensions and add basic support.

.gitignore

@@ -50,3 +50,6 @@ gradle-app.setting
 # gradle/wrapper/gradle-wrapper.properties
 
 /src/main/java/com/mcecraft/
+
+# When running the demo we generate the extensions folder
+extensions/

src/main/java/net/minestom/server/MinecraftServer.java

@@ -13,6 +13,8 @@ import net.minestom.server.data.DataType;
 import net.minestom.server.data.SerializableData;
 import net.minestom.server.entity.EntityManager;
 import net.minestom.server.entity.EntityType;
+import net.minestom.server.extensions.Extension;
+import net.minestom.server.extensions.ExtensionManager;
 import net.minestom.server.extras.mojangAuth.MojangCrypt;
 import net.minestom.server.fluids.Fluid;
 import net.minestom.server.gamedata.loottables.LootTableManager;
@@ -33,7 +35,6 @@ import net.minestom.server.network.packet.server.play.PluginMessagePacket;
 import net.minestom.server.network.packet.server.play.ServerDifficultyPacket;
 import net.minestom.server.particle.Particle;
 import net.minestom.server.ping.ResponseDataConsumer;
-import net.minestom.server.plugins.PluginManager;
 import net.minestom.server.potion.PotionType;
 import net.minestom.server.recipe.RecipeManager;
 import net.minestom.server.registry.ResourceGatherer;
@@ -123,7 +124,7 @@ public class MinecraftServer {
     private static BiomeManager biomeManager;
     private static AdvancementManager advancementManager;
 
-    private static PluginManager pluginManager;
+    private static ExtensionManager extensionManager;
 
     private static UpdateManager updateManager;
     private static MinecraftServer minecraftServer;
@@ -180,7 +181,7 @@ public class MinecraftServer {
 
         updateManager = new UpdateManager();
 
-        pluginManager = PluginManager.getInstance();
+        extensionManager = new ExtensionManager();
 
         lootTableManager = new LootTableManager();
         tagManager = new TagManager();
@@ -452,8 +453,14 @@ public class MinecraftServer {
         updateManager.start();
         nettyServer.start(address, port);
         long t1 = -System.nanoTime();
-        pluginManager.loadPlugins();
-        LOGGER.info("Plugins loaded in " + (t1 + System.nanoTime()) / 1_000_000D + "ms");
+        extensionManager.loadExtensionJARs();
+        // Init extensions
+        // TODO: Extensions should handle depending on each other and have a load-order.
+        extensionManager.getExtensions().forEach(Extension::preInitialize);
+        extensionManager.getExtensions().forEach(Extension::initialize);
+        extensionManager.getExtensions().forEach(Extension::postInitialize);
+
+        LOGGER.info("Extensions loaded in " + (t1 + System.nanoTime()) / 1_000_000D + "ms");
         LOGGER.info("Minestom server started successfully.");
     }
 

src/main/java/net/minestom/server/extensions/Extension.java

@@ -0,0 +1,41 @@
+package net.minestom.server.extensions;
+
+import com.google.gson.JsonObject;
+import org.slf4j.Logger;
+
+public abstract class Extension {
+    private JsonObject description;
+    private Logger logger;
+
+    protected Extension() {
+
+    }
+
+    public void preInitialize() {
+
+    }
+
+    public abstract void initialize();
+
+    public void postInitialize() {
+
+    }
+
+    public void preTerminate() {
+
+    }
+
+    public abstract void terminate();
+
+    public void postTerminate() {
+
+    }
+
+    public JsonObject getDescription() {
+        return description;
+    }
+
+    protected Logger getLogger() {
+        return logger;
+    }
+}

src/main/java/net/minestom/server/extensions/ExtensionManager.java

@@ -0,0 +1,169 @@
+package net.minestom.server.extensions;
+
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import lombok.extern.slf4j.Slf4j;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+@Slf4j
+public class ExtensionManager {
+    private final Map<URL, URLClassLoader> extensionLoaders = new HashMap<>();
+    private final Map<String, Extension> extensions = new HashMap<>();
+    private final File extensionFolder = new File("extensions");
+
+    public ExtensionManager() {
+    }
+
+    public void loadExtensionJARs() {
+        if (!extensionFolder.exists()) {
+            if (!extensionFolder.mkdirs()) {
+                log.error("Could not find or create the extension folder, extensions will not be loaded!");
+                return;
+            }
+        }
+
+        for (File file : extensionFolder.listFiles()) {
+            if (file.isDirectory()) {
+                continue;
+            }
+            if (!file.getName().endsWith(".jar")) {
+                continue;
+            }
+            URLClassLoader loader;
+            try {
+                URL url = file.toURI().toURL();
+                loader = loadJar(url);
+                extensionLoaders.put(url, loader);
+            } catch (MalformedURLException e) {
+                log.error(String.format("Failed to get URL for file %s.", file.getPath()));
+                return;
+            }
+            InputStream extensionInputStream = loader.getResourceAsStream("extension.json");
+            if (extensionInputStream == null) {
+                log.error(String.format("Failed to find extension.json in the file '%s'.", file.getPath()));
+                return;
+            }
+            JsonObject extensionDescription = JsonParser.parseReader(new InputStreamReader(extensionInputStream)).getAsJsonObject();
+
+            String mainClass = extensionDescription.get("entrypoint").getAsString();
+            String extensionName = extensionDescription.get("name").getAsString();
+            
+            if (extensions.containsKey(extensionName.toLowerCase())) {
+                log.error(String.format("An extension called '%s' has already been registered.", extensionName));
+                return;
+            }
+
+            Class<?> jarClass;
+            try {
+                jarClass = Class.forName(mainClass, true, loader);
+            } catch (ClassNotFoundException e) {
+                log.error(String.format("Could not find main class '%s' in extension '%s'.", mainClass, extensionName), e);
+                return;
+            }
+
+            Class<? extends Extension> extensionClass;
+            try {
+                extensionClass = jarClass.asSubclass(Extension.class);
+            } catch (ClassCastException e) {
+                log.error(String.format("Main class '%s' in '%s' does not extend the 'extension superclass'.", mainClass, extensionName), e);
+                return;
+            }
+
+            Constructor<? extends Extension> constructor;
+            try {
+                constructor = extensionClass.getDeclaredConstructor();
+                // Let's just make it accessible, plugin creators don't have to make this public.
+                constructor.setAccessible(true);
+            } catch (NoSuchMethodException e) {
+                log.error(String.format("Main class '%s' in '%s' does not define a no-args constructor.", mainClass, extensionName), e);
+                return;
+            }
+            Extension extension = null;
+            try {
+                // Is annotated with NotNull
+                extension = constructor.newInstance();
+            } catch (InstantiationException e) {
+                log.error(String.format("Main class '%s' in '%s' cannot be an abstract class.", mainClass, extensionName), e);
+                return;
+            } catch (IllegalAccessException ignored) {
+                // We made it accessible, should not occur
+            } catch (InvocationTargetException e) {
+                log.error(
+                        String.format(
+                                "While instantiating the main class '%s' in '%s' an exception was thrown.", mainClass, extensionName
+                        ), e.getTargetException()
+                );
+                return;
+            }
+            // Set description
+            try {
+                Field descriptionField = extensionClass.getSuperclass().getDeclaredField("description");
+                descriptionField.setAccessible(true);
+                descriptionField.set(extension, extensionDescription);
+            } catch (IllegalAccessException e) {
+                // We made it accessible, should not occur
+            } catch (NoSuchFieldException e) {
+                log.error(String.format("Main class '%s' in '%s' has no description field.", mainClass, extensionName), e);
+                return;
+            }
+            // Set Logger
+            try {
+                Field descriptionField = extensionClass.getSuperclass().getDeclaredField("logger");
+                descriptionField.setAccessible(true);
+                descriptionField.set(extension, LoggerFactory.getLogger(extensionClass));
+            } catch (IllegalAccessException e) {
+                // We made it accessible, should not occur
+            } catch (NoSuchFieldException e) {
+                log.error(String.format("Main class '%s' in '%s' has no logger field.", mainClass, extensionName), e);
+            }
+
+            extensions.put(extensionName.toLowerCase(), extension);
+        }
+    }
+
+    /**
+     * Loads a URL into the classpath.
+     *
+     * @param url {@link URL} (usually a JAR) that should be loaded.
+     */
+    @NotNull
+    public URLClassLoader loadJar(@NotNull URL url) {
+        return URLClassLoader.newInstance(new URL[]{url}, ExtensionManager.class.getClassLoader());
+    }
+
+    @NotNull
+    public File getExtensionFolder() {
+        return extensionFolder;
+    }
+
+    @NotNull
+    public List<Extension> getExtensions() {
+        return new ArrayList<>(extensions.values());
+    }
+
+    @Nullable
+    public Extension getExtension(@NotNull String name) {
+        return extensions.get(name.toLowerCase());
+    }
+
+    @NotNull
+    public Map<URL, URLClassLoader> getExtensionLoaders() {
+        return new HashMap<>(extensionLoaders);
+    }
+}

src/main/java/net/minestom/server/plugins/Plugin.java

@@ -1,5 +0,0 @@
-package net.minestom.server.plugins;
-
-public abstract class Plugin {
-
-}

src/main/java/net/minestom/server/plugins/PluginDescription.java

@@ -1,8 +0,0 @@
-package net.minestom.server.plugins;
-
-public @interface PluginDescription {
-
-	String name();
-	String description();
-	String version();
-}

src/main/java/net/minestom/server/plugins/PluginLoader.java

@@ -1,70 +0,0 @@
-package net.minestom.server.plugins;
-
-import lombok.extern.slf4j.Slf4j;
-
-import java.io.IOException;
-import java.lang.reflect.Type;
-import java.net.URL;
-import java.net.URLClassLoader;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.Enumeration;
-import java.util.List;
-import java.util.jar.JarEntry;
-import java.util.jar.JarFile;
-
-@Slf4j
-public class PluginLoader {
-
-	private static PluginLoader instance = null;
-
-	//Singleton
-	public static PluginLoader getInstance() {
-		if (instance == null) {
-			instance = new PluginLoader();
-		}
-		return instance;
-	}
-
-	private PluginLoader() {
-
-	}
-
-	public List<Plugin> loadPlugin(String path) {
-		JarFile jarFile;
-		URLClassLoader cl;
-		try {
-			jarFile = new JarFile(path);
-			URL[] urls = new URL[]{new URL("jar:file:" + path + "!/")};
-			cl = URLClassLoader.newInstance(urls);
-		} catch (IOException e) {
-			e.printStackTrace();
-			return new ArrayList<>();
-		}
-		final List<Plugin> plugins = new ArrayList<>();
-		final Enumeration<JarEntry> e = jarFile.entries();
-		while (e.hasMoreElements()) {
-			try {
-				final JarEntry je = e.nextElement();
-				if (je.isDirectory() || !je.getName().endsWith(".class")) continue;
-				// -6 because of .class
-				String className = je.getName().substring(0, je.getName().length() - 6);
-				className = className.replace('/', '.');
-				final Class<?> c;
-				c = cl.loadClass(className);
-				Type superclass = c.getGenericSuperclass();
-				if (superclass != null && Plugin.class.getTypeName().equals(superclass.getTypeName()))
-					try {
-						plugins.add((Plugin) c.getConstructor().newInstance());
-					} catch (final ReflectiveOperationException | ArrayIndexOutOfBoundsException ex) {
-						ex.printStackTrace();
-					}
-			} catch (final Throwable ex) {
-				ex.printStackTrace();
-			}
-		}
-
-		return Collections.unmodifiableList(plugins);
-	}
-
-}

src/main/java/net/minestom/server/plugins/PluginManager.java

@@ -1,43 +0,0 @@
-package net.minestom.server.plugins;
-
-import lombok.extern.slf4j.Slf4j;
-
-import java.io.File;
-
-@Slf4j
-public class PluginManager {
-
-	private static PluginManager instance = null;
-
-	//Singleton
-	public static PluginManager getInstance() {
-		if (instance == null) {
-			instance = new PluginManager();
-		}
-		return instance;
-	}
-
-	private final PluginLoader loader = PluginLoader.getInstance();
-
-	private final File pluginsDir;
-
-	private PluginManager() {
-		pluginsDir = new File("plugins");
-		if (!pluginsDir.exists()||!pluginsDir.isDirectory()) {
-			if (!pluginsDir.mkdir()) {
-				log.error("Couldn't create plugins dir, plugins will not be loaded.");
-				return;
-			}
-		}
-	}
-
-	public void loadPlugins() {
-
-		File[] files = pluginsDir.listFiles();
-		if(files != null) {
-			for (final File plugin : files) {
-				loader.loadPlugin(plugin.getPath());
-			}
-		}
-	}
-}